For example, JP 2009-508760T (Reference 1) and US 2010/0194125A (Reference 2) disclose a crash box which is provided between a bumper reinforcement and a side member (a member of a vehicle body side), and installed to the bumper reinforcement. The crash box disclosed in References 1 and 2 includes two plate-shaped support sections which are provided in the front end side thereof and separated from each other in the vertical direction, and the bumper reinforcement is inserted between the two support sections. In addition, the support sections of the crash box and the bumper reinforcement have mounting holes, and the bumper reinforcement is inserted between the support sections of the crash box so that center axes of the mounting holes match with each other. Then, a bolt is inserted into the mounting holes from one of the support sections, front end side of the bolt is outwardly exposed from the other of the support sections and the exposed front end side of the bolt is fastened by a nut. In this way, the crash box is installed to the bumper reinforcement by inserting the bumper reinforcement between the support sections.
If the bumper reinforcement is open forwards or rearwards, in other words, if a cross-section perpendicular to the extending direction of the bumper reinforcement is an open cross-section, when the bolts are fastened to fix the crash box to the bumper reinforcement, the bumper reinforcement and the support sections may be deflected due to a fastening force. Thus, a fastening torque of the bolt cannot be too large and the bumper reinforcement cannot be firmly fixed to the crash box. If the bumper reinforcement is not open forwards and rearwards, in other words, if the cross-section perpendicular to the extending direction of the bumper reinforcement is a closed cross-section, the deflection described above can be prevented, however, the weight of the bumper reinforcement is increased. In addition, in this case, the material cost is high compared to the case where the cross-section perpendicular to the extending direction of the bumper reinforcement is the open cross-section.
A need thus exists for a crash box and a bumper device which is not susceptible to the drawback mentioned above.